Synthesis and brain in vitro studies of a broad series of Beta-carbolines and related compounds have established a relatively clear structural-activity relationship in this series. Optimum binding was observed in the fully aromatic Beta-carboline series when an ester or ketone carbonyl group was present at C-3. The 3-acetyl and 3-formyl derivatives were benzodiazepine antagonists in vivo (mice). A biomimetic Pictet-Spengler approach was used to prepare several imidazopyridines which showed moderate affinity for the benzodiazepine receptor.